Recurrence interval of riverbed sand mining hotspots in the Mekong delta: Potential indications of unsustainable replenishment rates.

Rampant and illegal river sand mining in the Vietnamese Mekong Delta (VMD) has led to substantial sediment losses and bank erosion. However, regulation of this issue remains a significant challenge due to insufficient monitoring and enforcement efforts, partly attributed to limited data and technology. To support an improved monitoring system in the VMD, this study investigates the spatiotemporal changes in sand mining hotspots and their underlying drivers. The recurrence intervals of sand mining boats were assessed from 2014 to 2020 using Sentinel-1A, and its association with riverbed incisions were examined from bathymetry field surveys between 2017 and 2020. Our results attest to sand mining intensification from 2015 to 2020, particularly in the upstream section of the VMD, where 70% of the activity was recorded. Not only was there an apparent increase in sand mining hotspots by 32.4%, but most hotspots recorded a recurrence interval of 2 years. This potentially indicates a minimal timeframe of sediment replenishment before the same locations become economically viable for further sand extraction. Additionally, a correlation was detected between sand mining hotspots and significant riverbed incisions, although the lack of spatial overlaps in some regions suggests other upstream influences like bank collapse and river damming. Our study, through the meticulous assessment of sand mining boat movement and river bathymetry data, ultimately sheds light on the potentially unsustainable scale of sand mining activities in the VMD. It aims to support informed decision-making and effective regulations that tackle excessive sand extraction amid the dynamic environmental challenges we face, while offering valuable insights to similar deltas worldwide.

The Great 2011 Thailand flood disaster revisited: Could it have been mitigated by different dam operations based on better weather forecasts?

This paper revisits the 2011 Great Flood in central Thailand to answer one of the hotly debated questions at the time "Could the operation decisions of the flood control structures substantially mitigate the flood impacts in the downstream areas?". Using a numerical modeling approach, we develop a hypothesis such that the two upstream dam reservoirs: Bhumibol and Sirikit had more accurately forecasted the typhoon-triggered abnormal rainfall volumes and released more water earlier to save the storage capacity via 17 different scenarios or alternative operation schemes. We subsequently quantify the potential improvements, or reduced flood impacts in the downstream catchments, solely by changing the operation schemes of these two dam reservoirs, with all other conditions remaining unchanged. We observed that changing the operation schemes could have reduced only the flood depth while offering very limited improvements in terms of inundated areas for the lower Chao Phraya River Basin. Among 17 scenarios simulated, the inundated areas could have been reduced at most by 3.68%. This result justifies the limited role of these mega structures in the upstream during the disaster on one hand, while pointing to the necessity of handling local rainfall differently on the other. The paper expands the discussion into how the government of Thailand has drawn the lessons from the 2011 flood to better prepare themselves against the lurking flood risk in 2021, also triggered by tropical cyclones. The highlighted initiatives, both technical and institutional, could have provided important references for the large river catchment managers in Southeast Asia and with implications of our method beyond the present application region.

Deep well injection for the waste brine disposal solution of potash mining in Northeastern Thailand.

Under the pressure of the existing world population growth trends, the dercreasing pastoral fields and the increasing duration and incidences of drought and heat stress, the potash fertilizers demand dramaticly increase to enhance the world food production. Asia currently consumes 40% of the world's potash market, yet 70% of world potash exports come from mines in Canada and Europe. Weak collective efforts to produce potassium fertilizers economically pose the risk of global shortages of potash goods and threatening global food security. While the Khorat Plateau in Northeastern Thailand is noted to contain active and promising regional potash deposits, developing a proper potash industry in the region has largely been unsuccessful due to major constraints such as the challenge of establishing a brine disposal solution. This study demonstrates the performance of deep well injection (DWI) as an environmentally friendly alternative to secure waste brine production from the potash mine. The groundwater numerical model demonstrates the movement and penetration of the concentrate during and after deep well injection. The boundary condition was utilized from the regional hydrogeology data. The waste brine injection is based on the waste products of the mine factory. Our simulation shows that the DWI can isolate waste brine with freshwater by injecting it into the deep formation based on the geologic structure and properties analysis. With high porosity and low specific yield, the Khok Kruat formation within Khrat Basin shows a high potential injection rate of 200,000 m3/day, which is 200 times higher than current water brine production rates. Moreover, the salinity can easily dissolve into the target domain with specific formation properties. Hence, the DWI not only boosts the potash industry's image in the long term but also enable sustainable potash mining development in the region. Finally, we recommend that government agencies with regulatory oversight over the DWI must promote further research associated with site characterization, well construction and injection technologies, and monitoring tools in the long term.

Spatial-social evaluations of ecosystem services of adaptive aquaculture models using SAR and multivariate analyses: a case in the Vietnamese Mekong Delta.

The presented study is conducted to investigate the efficiency of two important aquaculture models of the Vietnamese Mekong Delta (VMD)'s Soc Trang province via quantifying and mapping the supporting ecosystem services (ES). The study targets the two most prevalent rearing practices, intensive and semi-intensive, covering four rural districts: My Xuyen, Tran De, Cu Lao Dung, and Vinh Chau. A mixed-method approach was applied, combining remote sensing, grass-root social survey, and multivariate statistical analyses. First, image analysis using Sentinel-1A time-series data was conducted to detect the aquaculture areas across the study area based on temporal changes of VV backscatter of different land use/land cover (LULC) types, in which aquaculture receives relatively low backscatter values compared to other LULC categories except river and deeper water surfaces. Our analysis yields an overall accuracy of 91% with a kappa coefficient of 0.82. Second, using semi-structured questionnaires, a total of 140 shrimp farming households across the four focused districts were interviewed for their rearing experience. Thereupon, the collected responses were analyzed using two multivariate analyses, including principal component analysis (PCA) and hierarchical cluster analysis (HCA). In general, the intensive model could have generated more economic values of ecosystem services than the artisanal/semi-intensive model. Our analyses also took note of the potential barriers hindering the semi-intensive farmers from achieving higher economic income. These include (i) geographical factors, i.e., locations; (ii) social factors, i.e., experience, farming calendar, education; (iii) financial factors, i.e., investments; and (iv) technical factors, i.e., farm areas, productivity, rearing concentration. Since semi-intensive food is more appropriate for small-scale farming households, it is recommendable that addressing these factors can enhance the efficiency of this model as a profitable livelihood option.

Socio-geographical evaluation of ecosystem services in an ecotourism destination: PGIS application in Tram Chim National Park, Vietnam.

Ecotourism in national parks of developing countries is increasingly recognised as a promising option to achieve sustainable development goals, regardless, might imply various paradoxical managerial challenges. This paper, therefore, seeks to contribute a methodological framework utilising ES-based social landscape metrics (SLM) to address the potential barriers in managing ecotourism-integrated multi-functional national parks. We present a mixed-method case study in Vietnam's Tram Chim National Park (TCNP), conducted via semi-structural interviews and PGIS with tourists and locals. Multiple key informants, i.e. TCNP's authorities were also interviewed to provide their managerial insights and assist in verifying the PGIS results obtained from the tourists and locals. Via the quantified and mapped SLMs, the study reveals the differences between tourists and locals in terms of how and where they perceive and appreciate the intangible values of TCNP. Through spatial statistics, we reported important spatial correlations (i) between different categories of Ecosystem Services (ES) and (ii) between ES richness and diversity on different TCNP's land covers. As a contribution to the decision-making outlook, we remarked potential areas to expand of ecotourism activities based on the spatial hot and cold spots. This study concludes by highlighting opportunities for future research in expanding on socio-geographical assessments of ES, especially in the fields of ecotourism.

Mapping the vulnerability of irrigation sand traps in a tropical volcanic basin, Indonesia.

Sand traps in irrigation networks are typically used in mitigating canal sedimentation. In irrigation networks located in basins of high sediment yield due to the presence of volcanoes, it is essential to assess the vulnerability of sand traps. Using sediment yield at irrigation scheme inlets, sand trap vulnerability can be evaluated. This study aims to understand the vulnerability of irrigation sand traps throughout the Progo-Opak-Serang (POS) Volcanic River Basin, Indonesia, via mapping the sediment yield distributions in the basin. We employed the Revised Universal Soil Loss Equation to estimate soil loss, where the results show that the average soil loss in the POS River Basin is 179.69 tons/ha/year that falls under the category of moderate erosion potential, while the average sediment yield for the whole basin is 51.04 tons/ha/year. Parts of the basin with high yields of more than 180 tons/ha/year were mostly found along the volcanic mountains such as Sindoro, Sumbing, Merapi, Merbabu, and Telomoyo, and the Menoreh Hills. The model demonstrated relatively high performance with R2, NSE, RMSE, and MAE of 0.89, 0.82, 0.14, and 0.11, respectively. Within the POS Basin, Badran, Kalibawang, and Blawong are the three most vulnerable irrigation sand traps, with sediment yield values of 252.83, 178.92, and 63.49 tons/ha/year, respectively; they are all located in sub-watershed outlets. The vulnerability assessment conducted in this study can be used for the decision support system to prioritize irrigation sand traps towards a more effective irrigation system development.

A synthesis of hydroclimatic, ecological, and socioeconomic data for transdisciplinary research in the Mekong.

The Mekong River basin (MRB) is a transboundary basin that supports livelihoods of over 70 million inhabitants and diverse terrestrial-aquatic ecosystems. This critical lifeline for people and ecosystems is under transformation due to climatic stressors and human activities (e.g., land use change and dam construction). Thus, there is an urgent need to better understand the changing hydrological and ecological systems in the MRB and develop improved adaptation strategies. This, however, is hampered partly by lack of sufficient, reliable, and accessible observational data across the basin. Here, we fill this long-standing gap for MRB by synthesizing climate, hydrological, ecological, and socioeconomic data from various disparate sources. The data- including groundwater records digitized from the literature-provide crucial insights into surface water systems, groundwater dynamics, land use patterns, and socioeconomic changes. The analyses presented also shed light on uncertainties associated with various datasets and the most appropriate choices. These datasets are expected to advance socio-hydrological research and inform science-based management decisions and policymaking for sustainable food-energy-water, livelihood, and ecological systems in the MRB.

The worst 2020 saline water intrusion disaster of the past century in the Mekong Delta: Impacts, causes, and management implications.

Vietnam Mekong Delta (VMD), the country's most important food basket, is constantly threatened by drought-infused salinity intrusion (SI). The SI disaster of 2020 is recognized as the worst in recent decades, hence inspiring this perspective article. The authors' viewpoints on the disaster's impacts and causes are presented. The arguments presented are mainly drawn from (i) up-to-date publications that report on the recent SI intensification in the VMD and (ii) the power spectral analysis results using water level data. We verified the intensifying SI in the VMD both in its frequency and magnitude and remarked on four of the key SI drivers: (i) upstream hydropower dams, (ii) land subsidence, (iii) the relative sea-level rise, and (iv) riverbed sand mining. Also, a non-exhaustive yet list of recommendable management implications to mitigate the negative effects of the SI is contributed. The mitigation measures must be realized at multiple scales, ranging from pursuing transboundary water diplomacy efforts to managing internal pressures via developing early warnings, restricting illegal sand mining activities, alleviating pressures on groundwater resources, and diversifying agriculture.

How the saline water intrusion has reshaped the agricultural landscape of the Vietnamese Mekong Delta, a review.

Once a key factor behind Vietnam's successful Doi Moi (restoration) economic reforms, the rice-centered agriculture of the VMD is now confronted by the new pressure of climate change impacts, including the intensifying salinity intrusion (SI). The SI menace has partly triggered the delta-wide emergence of new adaptive livelihood models across the VMD, including the prawn rice rotational crop (PRRC) that is arguably the most prominent. Research on the SI-driving factors is rapidly increasing in numbers, yet little synthesis has been done. Likewise, several studies have investigated the economic benefits of PRRC; less emphasis has placed on environmental and societal aspects, hence the questionable sustainability. This study, therefore, contributes a composite literature review, targeting two SI-related aspects: (i) key factors driving the intensification of SI in recent years across the Mekong Delta, and (ii) current understanding of the sustainability of PRRC. Results from the first review assignment highlight the four key SI-driving factors: riverbed incision, land subsidence, upstream dams, and sea-level rise. Also remarked are the critical absence of studies addressing multiple drivers and the need for a decoupling model to quantify the relative importance of each factor to strategize the adaptive measures. For PRRC, we reveal that while economic benefits have been widely reported, potential negative impacts of this model related to environmental and social aspects are lacking. Therefore, while the lucrative prawn trade might financially benefit the farmers', the economic benefit is marred by the underlying negative environmental impacts and social inequalities, limiting overall sustainability. This study also provides a case study to notify the spatial-temporal trends of PRRC in the last three decades and evaluate the associated geographical and social factors. Kien Giang province was selected as the study site since it is the largest PRRCacross the VMD. The lessons from Kien Giang can also be applied to other transformative agricultural models in both Mekong Delta and other deltas worldwide.

Intensifying saline water intrusion and drought in the Mekong Delta: From physical evidence to policy outlooks.

This paper assesses the recently intensified saline water intrusion (SI) and drought in the Vietnamese Mekong Delta (VMD). While the existing literature predominantly points the cause of drought to the hydropower dams in the upstream of the Mekong Basin, we contribute new physical evidence of the intensification of saline water intrusion (through backwater effect) in the VMD caused by three anthropogenic drivers: riverbed incision (due to both riverbed mining and dam construction), sea level rise and land subsidence. Thereupon, we highlight that it is critical to not underestimate the impacts from the localized factors, especially the riverbed-mining which can incise the channel by up to 15 cm/year and amplify the salinity intrusion. Our analysis is based on the extensive sets of hourly-to-daily hydrological time series from 11 gauge stations across the VMD. First, several signs of significantly increased tidal amplification (up to 66%) were revealed through the spectral analysis of the hourly water level data. This trend was further validated through the changes in slopes of the rating curves at the tidal zones, implying the relationships between the shift of the backwater effects on the rivers in VMD and the lowered water levels caused by the riverbed incision. Finally, we introduce a novel approach using the annual incision rates of the riverbed to compare four SI driving factors in terms of their relative contributions to the balance between fresh and saline water in the VMD.